U.S. patent number 6,555,183 [Application Number 09/495,555] was granted by the patent office on 2003-04-29 for plasma treatment of a titanium nitride film formed by chemical vapor deposition.
This patent grant is currently assigned to Applied Materials, Inc.. Invention is credited to Mei Chang, Zvi Lando, Shulin Wang, Ming Xi.
United States Patent |
6,555,183 |
Wang , et al. |
April 29, 2003 |
**Please see images for:
( Certificate of Correction ) ** |
Plasma treatment of a titanium nitride film formed by chemical
vapor deposition
Abstract
A method of forming thick titanium nitride films with low
resistivity. Using a thermal chemical vapor deposition reaction
between ammonia (NH.sub.3) and titanium tetrachloride (TiCl.sub.4),
a titanium nitride film is formed at a temperature of less than
about 600.degree. C., and an NH.sub.3 :TiCl.sub.4 ratio greater
than about 5. The deposited TiN film is then treated in a
hydrogen-containing plasma such as that generated from molecular
hydrogen (H.sub.2). This results in a thick titanium nitride film
with low resistivity and good step coverage. The deposition and
plasma treatment steps may be repeated for additional cycles to
form a thick, composite titanium nitride film of desired thickness,
which is suitable for use in plug fill or capacitor structure
applications.
Inventors: |
Wang; Shulin (Campbell, CA),
Xi; Ming (Milpitas, CA), Lando; Zvi (Palo Alto, CA),
Chang; Mei (Saratoga, CA) |
Assignee: |
Applied Materials, Inc. (Santa
Clara, CA)
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Family
ID: |
23969078 |
Appl.
No.: |
09/495,555 |
Filed: |
February 1, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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330696 |
Jun 11, 1999 |
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Current U.S.
Class: |
427/535;
257/E21.17; 257/E21.585; 427/255.391; 427/255.394 |
Current CPC
Class: |
C23C
16/34 (20130101); H01L 21/28556 (20130101); H01L
21/76843 (20130101); H01L 21/76846 (20130101); H01L
21/76862 (20130101); H01L 21/76877 (20130101); H01L
28/75 (20130101) |
Current International
Class: |
C23C
16/34 (20060101); H01L 21/285 (20060101); H01L
21/768 (20060101); H01L 21/70 (20060101); H01L
21/02 (20060101); C23C 016/50 () |
Field of
Search: |
;427/535,255.391,255.394 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0 711 846 |
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May 1996 |
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EP |
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63-229814 |
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Sep 1988 |
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JP |
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10-209278 |
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Sep 1998 |
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JP |
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95/33865 |
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Dec 1995 |
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WO |
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Other References
Bouteville et al. "Low Temperature Rapid Thermal Low Pressure
Chemical Vapor Deposition of (111) Oriented TiN Layers from the
TiCI.sub.4 -NH.sub.3 -H.sub.2 Gaseous Phase" Microelectronic
Enginerring 37/38, pp. 421-425, 1997.* .
Erkov et al. "Deposition and Properties of Titanium Nitride Films
Obtained by TiCI.sub.4 Ammonolysis in the LPCVD Process" Russian
Microelectronics, vol. 27, No. 3, pp. 183-187, 1998.* .
Gross et al."Effect of NH, Plasma Treatment on Etching of Ti During
TiCI.sub.4 -Based TiN CVD Processes" Mat. Res. Soc. Symp. Proc.,
vol. 514, pps. 523-529, 1998. .
Buiting et al "Kinetical Aspects of the LPCVD of Titanium Nitride
from Titanium Tetrachloride and Amonia" J. Electrochem. Soc., vol.
138, No. 2, pps. 500-505, Feb. 1991. .
Mori et al. "Contact Plug Formed with Chemical-Vapour-Deposited
TiN" Abstracts of the 1991 International Conference on Solid State
Devices and Materials, pps. 210-212, 1991. .
Yokoyama et al. "LPCVD Titanium Nitride for ULSIs" J. Electrochem
Soc., vol. 138, No. 1, pps. 190-195, Jan. 1991. .
Kurtz e t al. "Chemical Vapor Deposition of Titanium Nitride at Low
Temperatures" Thin Solid Films, vol. 140, pps. 277-290, 1985. .
Kim et al "The Effect of In-Situ N2/H2 Plasma Treatment on the
Properties of Chemically Vapor Deposited TiN" Electrochemical
Society Proceedings, vol. 97-25, pp. 1626-1633 (1997). .
Kim et al "Effect of N.sub.2 /H.sub.2 Plasma Treatment on the
Properties in TiN Films Prepared by Chemical Vapor Deposition from
TiCI.sub.4 and NH.sub.3 ", Jpan. J. Appl. Phys., vol. 38, pp.
461-463, Part 2, No. 4B, Apr. 15, 1999. .
Konecni et al "A Stable Plasma Treated CVD Titanium Nitride Film
for Barrier/Glue Layer Applications" VMIC Conference, pp. 181-183,
Jun. 18-20, 1996. .
Arena et al "A New Low Temperature PECVD TiN Compatible with
Multilevel Vias Application" VMIC Conference, pp. 566-571, Jun.
18-20, 1996..
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Primary Examiner: Meeks; Timothy
Attorney, Agent or Firm: Moser Patterson Sheridan
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part of commonly assigned
U.S. patent application, Ser. No. 09/330,696, entitled "Method of
Depositing a Thick Titanium Nitride Film", filed on Jun. 11, 1999,
which is incorporated herein by reference.
Claims
What is claimed is:
1. A method of depositing a titanium nitride layer, comprising the
steps of: (a) forming a titanium nitride layer upon a substrate
inside a processing chamber using a thermal reaction between
ammonia (NH.sub.3) and titanium tetrachloride (TiCl.sub.4) at a
pressure range of about 10 to about 50 torr and a temperature of
less than about 600.degree. C.; and (b) following said step (a),
treating said titanium nitride layer in a plasma generated from a
gas consisting of molecular hydrogen (H.sub.2) without removing
said substrate from said processing chamber, wherein the plasma is
generated at a temperature between about 500.degree. C. to about
600.degree. C.
2. The method of claim 1, wherein said step (b) is performed at a
pressure of about 0.5 torr. to about 10 torr.
3. The method of claim 1, wherein said step (a) is performed at an
NH.sub.3 :TiCl.sub.4 flow ratio greater than about 5.
4. The method of claim 1, wherein said titanium nitride layer
formed in said step (a) has a thickness of less than about 300
.ANG..
5. The method of claim 1, wherein said titanium nitride layer has a
film resistivity of less than about 200 .mu.ohm-cm after said step
(b).
6. The method of claim 1, further comprising the step of: (c)
repeating said steps (a) and (b) to form a composite titanium
nitride layer having a thickness of at least 1000 .ANG., and a
resistivity less than about 200 .mu.ohm-cm.
7. The method of claim 1, wherein said plasma of step (b) is a
radio-frequency plasma.
8. The method of claim 1, wherein said plasma of step (b) is a
remote plasma.
9. A method of depositing a titanium nitride layer comprising the
steps of: (a) forming a first titanium nitride layer upon a
substrate inside a processing chamber using a thermal reaction
between ammonia (NH.sub.3) and titanium tetrachloride TiCl1.sub.4)
at a first NH.sub.3 :TiCl.sub.4 flow ratio of greater than about
20, within a pressure range of about 1.0 to about 50 torr and a
temperature of less than about 600.degree. C.; (b) forming a second
titanium nitride layer upon said first titanium nitride layer of
step (a) using a thermal reaction between NH.sub.3 and TiCl.sub.4
at a second NH.sub.3 :TiCl.sub.4 flow ratio different from said
first NH.sub.3 :TiCl.sub.4 flow ratio used in said step (a); and
(c) following said step (b), exposing said second titanium nitride
layer to a plasma generated from a gas consisting of molecular
hydrogen (H.sub.2), without removing said substrate from said
processing chamber.
10. The method of claim 9, wherein said first titanium nitride
layer has a thickness less than about 20 .ANG., said second
titanium nitride layer has a thickness of less than about 300 .ANG.
and said second NH.sub.3 :TiCl.sub.4 flow ratio is greater than
about 5.
11. The method of claim 9, wherein said steps (a), (b) and (c) are
repeated for additional cycles to form a composite titanium nitride
layer of thickness greater than about 1000 .ANG..
12. The method of claim 9, wherein said plasma of step (c) is a
radio frequency plasma.
13. The method of claim 9, wherein the plasma of step (c) is a
remote plasma.
14. A method of forming a capacitor structure, comprising the steps
of: (a) forming a first electrode upon a substrate; (b) forming an
insulating layer upon said first electrode; (c) forming a titanium
nitride layer upon said insulating layer using a thermal reaction
between ammonia (NH.sub.3) and titanium tetrachloride (TiCl.sub.4)
at a pressure range of about 10 to about 50 torr and a temperature
of less than about 600.degree. C.; (d) exposing said titanium
nitride layer formed in step (c) to a plasma generated from a gas
consisting of molecular hydrogen (H.sub.2); and (e) forming a
second electrode upon said titanium nitride layer after step
(d).
15. The method of claim 14, wherein said insulating layer of step
(b) comprises tantalum pentoxide (Ta.sub.2 O.sub.5).
16. The method of claim 14, wherein said step (c) is performed at
an NH.sub.3 :TiCl.sub.4 flow ratio greater than about 5.
17. The method of claim 14, wherein said first electrode comprises
silicon.
18. The method of claim 14, wherein said second electrode comprises
silicon.
Description
BACKGROUND OF THE DISCLOSURE
1. Field of the Invention
The invention relates to a method of titanium nitride film
deposition and, more particularly, to a method of forming a thick,
low stress titanium nitride film having low resistivity.
2. Description of the Background Art
In the manufacture of integrated circuits, a titanium nitride film
is often used as a metal barrier layer to inhibit the diffusion of
metals into an underlying region beneath the barrier layer. These
underlying regions include transistor gates, capacitor dielectric,
semiconductor substrates, metal lines, and many other structures
that appear in integrated circuits.
A combination of titanium/titanium nitride (Ti/TiN) is often used
as a diffusion barrier and provides contacts to the source and
drain of a transistor. In forming a contact using a tungsten (W)
plug process, for example, a Ti layer is deposited upon a silicon
(Si) substrate, followed by conversion of the Ti layer into
titanium silicide (TiSi.sub.x), which provides a lower resistance
contact with Si. A TiN layer is then formed upon the TiSi.sub.x
layer, prior to forming the tungsten plug. Alternatively, in some
applications, a TiN plug may also be formed instead of a W
plug.
Ti and TiN films can be formed by physical or chemical vapor
deposition. A Ti/TiN combination layer may be formed in a multiple
chamber "cluster tool" by depositing a Ti film in one chamber
followed by TiN film deposition in another chamber. When depositing
both Ti and TiN using chemical vapor deposition (CVD), titanium
tetrachloride (TiCl.sub.4), for example, may be used to form both
Ti and TiN films when allowed to react with different reactant
gases, i.e., under plasma conditions, Ti is formed when TiCl.sub.4
reacts with H.sub.2, and TiN is formed when TiCl.sub.4 reacts with
nitrogen. In general, TiN can be formed by reacting TiCl.sub.4 with
a nitrogen-containing compound under either plasma or thermal
conditions, depending on the specific nitrogen-containing compound.
Thus, a TiN film may be formed by high temperature CVD using a
reaction between TiCl.sub.4 and ammonia (NH.sub.3). However,
thicker TiN films deposited using some prior art processes tend to
develop cracks, especially when the film thickness exceeds about
400 .ANG.. With increasing film thickness, both the density and
size of the cracks increase, until the film eventually peels
off.
Furthermore, when a TiN film is deposited from a TiCl.sub.4 -based
chemical process, chlorine (Cl) is entrained in the TiN layer. The
Cl content has been associated with an increase in film
resistivity, which in turn results in an undesirable increase in
contact resistance. For TiN plug applications, a TiN film thickness
of over 1000 .ANG. is often required, and a reduction of film
resistivity becomes even more important.
Although the Cl content in the deposited TiN film can be reduced by
increasing the deposition temperature, improved step coverage is
favored by lowering the deposition temperature. Furthermore, a
relatively low deposition temperature is advantageous for process
integration purposes. For example, TiN can be used as a barrier
layer for an upper electrode in a capacitor structure with tantalum
pentoxide (Ta.sub.2 O.sub.5) as the dielectric. However, thermal
CVD of TiN--e.g., using a reaction between TiCl.sub.4 and NH.sub.3,
is often performed at a temperature of about 650.degree. C. Such a
high temperature may cause undesirable atomic inter-diffusion
within the capacitor structure.
Therefore, a need exists in the art for a method of depositing TiN
at a reduced temperature, to yield thick, crack-free TiN films
having improved properties including good step coverage and low
resistivity.
SUMMARY OF THE INVENTION
The present invention is a method of forming a titanium nitride
(TiN) layer using a reaction between ammonia (NH.sub.3) and
titanium tetrachloride (TiCl.sub.4) at a pressure of about 10 to
about 50 torr and a temperature of less than about 600.degree. C.,
followed by treating the TiN layer in a hydrogen-containing
plasma.
In one embodiment of the present invention, the TiN layer is formed
at a pressure of about 20 torr and a temperature between about
550.degree. C. and about 600.degree. C. at an NH.sub.3 :TiCl.sub.4
flow ratio of about 8.5, followed by in situ plasma treatment in
the presence of H.sub.2. Under these process conditions, a TiN
layer of at least 250 .ANG. can be formed. By repeating the TiN
deposition and plasma treatment for additional cycles, a composite
TiN layer of desired thickness can be formed for plug-fill
applications. The method of the present invention can also be used
to form a TiN layer as part of an upper electrode in a capacitor
structure. The treatment of the TiN layer may be performed using a
radio-frequency (RF) local plasma or a remote plasma.
In an alternative embodiment, alternate TiN layers can be formed
using different deposition conditions. For example, a second TiN
layer having step coverage and/or stress characteristics different
from the first TiN layer may be formed by using an NH.sub.3
:TiCl.sub.4 flow ratio that is different from that used in the
first TiN layer. By alternating between deposition and treatment of
the first and second TiN layers using different processing
conditions, a composite TiN layer of final desired thickness can be
achieved, with improved overall step coverage and stress
characteristics.
BRIEF DESCRIPTION OF THE DRAWINGS
The teachings of the present invention can be readily understood by
considering the following detailed description in conjunction with
the accompanying drawings, in which:
FIG. 1 is a schematic illustration of an apparatus that can be used
to practice this invention;
FIGS. 2a-2c depict schematic cross-sectional views of a substrate
structure with a titanium nitride layer being formed according to
one aspect of the present invention;
FIGS. 3a-3d depict schematic cross-sectional views of a substrate
structure at different stages of integrated circuit fabrication, in
which a composite titanium nitride layer is formed according to
another embodiment of the present invention;
FIG. 4 depicts a cross-sectional view of a capacitor structure
having a titanium nitride barrier layer that is formed in
accordance with the present invention; and
FIG. 5 depicts a schematic illustration of an alternative
embodiment of the apparatus of FIG. 1 that can be used to practice
this invention.
To facilitate understanding, identical reference numerals have been
used, where possible, to designate identical elements that are
common to the figures.
DETAILED DESCRIPTION
The present invention provides a method of forming a thick titanium
nitride (TiN is used generically to include films of different
stoichiometries) film with low resistivity and good step coverage.
A thick TiN film, for example, may be used for plug applications in
sub-0.18 .mu.m technology. Embodiments of the invention allow
relatively thick TiN films with low resistivity to be formed using
a reaction between NH.sub.3 and TiCl.sub.4 at a reduced deposition
temperature.
In one embodiment, a TiN layer is deposited at an NH.sub.3
:TiCl.sub.4 flow ratio in the range of about 2.5 to about 17,
typically above 5, and more preferably, about 8.5, and a process
temperature of less than about 600.degree. C., or preferably about
580.degree. C. The deposited TiN layer, having a thickness of up to
about 300 .ANG., is then exposed to a hydrogen-containing plasma.
The plasma-treated TiN layer has a reduced resistivity compared to
the as-deposited TiN layer due to a lower Cl content.
Alternatively, the TiN layer may be deposited in a two-step
procedure, in which a relatively thin TiN layer, e.g., less than
about 20 .ANG., is deposited using a first NH.sub.3 :TiCl.sub.4
flow ratio, followed by deposition of a second TiN layer using a
second NH.sub.3 :TiCl.sub.4 flow ratio. The resulting TiN layer is
then treated in a hydrogen-containing plasma to yield a thick TiN
layer with reduced resistivity.
Depending on the specific application, the film deposition and
plasma treatment steps can be repeated for additional cycles to
yield a composite TiN layer. For example, a thick TiN layer can be
obtained for thicknesses above 1000 .ANG.. The composite TiN layer
typically has.a resistivity of less than about 200 .mu.ohm-cm, and
is well-suited for plug-fill applications for geometries below 0.18
.mu.m.
System 10
FIG. 1 is a schematic representation of a wafer processing system
10 that can be used to practice embodiments of the present
invention. The system 10 comprises a process chamber 100, a gas
panel 130, a control unit 110, along with other hardware components
such as power supplies and vacuum pumps. One example of the process
chamber 100 is a TiN chamber, which has previously been described
in a commonly-assigned U.S. patent application entitled "High
Temperature Chemical Vapor Deposition Chamber," Ser. No.
09/211,998, filed on Dec. 14, 1998, and is herein incorporated by
reference. Some key features of the system 10 are briefly described
below.
Chamber 100
The process chamber 100 generally comprises a support pedestal 150,
which is used to support a substrate such as a semiconductor wafer
190 within the process chamber 100. This pedestal 150 can be moved
in a vertical direction inside the chamber 100 using a displacement
mechanism (not shown). Depending on the specific process, the wafer
substrate 190 has to be heated to some desired temperature prior to
processing. In the present invention, the wafer support pedestal
150 is heated by an embedded heater 170. For example, the pedestal
150 may be resistively heated by applying an electric current from
an AC supply 106 to the heater element 170. The wafer 190 is, in
turn, heated by the pedestal 150, and can be maintained within a
process temperature range of, for example, 400-750.degree. C. A
temperature sensor 172, such as a thermocouple, is also embedded in
the wafer support pedestal 150 to monitor the temperature of the
pedestal 150 in a conventional manner. For example, the measured
temperature may be used in a feedback loop to control the power
supply 106 for the heating element 170 such that the wafer
temperature can be maintained or controlled at a desired
temperature that is suitable for the particular process
application.
Proper control and regulation of the gas flows through the gas
panel 130 is performed by mass flow controllers (not shown) and a
controller unit 110 such as a computer. The showerhead 120 allows
process gases from the gas panel 130 to be uniformly distributed
and introduced into the chamber 100. Illustratively, the control
unit 110 comprises a central processing unit (CPU) 112, support
circuitry 114, and memories containing associated control software
116. This control unit 110 is responsible for automated control of
the numerous steps required for wafer processing--such as wafer
transport, gas flow control, temperature control, chamber
evacuation, and so on. Bi-directional communications between the
control unit 110 and the various components of the system 10 are
handled through numerous signal cables collectively referred to as
signal buses 118, some of which are illustrated in FIG. 1.
A vacuum pump 102 is used to evacuate the process chamber 100 and
to maintain the proper gas flows and pressure inside the chamber
100. A showerhead 120, through which process gases are introduced
into the chamber 100, is located above the wafer support pedestal
150. The "dual-gas" showerhead 120 used in the present invention
has two separate pathways, which allow two gases to be separately
introduced into the chamber 100 without premixing. Details of the
showerhead 120 have been disclosed in a commonly-assigned U.S.
patent application entitled "Dual Gas Faceplate for a Showerhead in
a Semiconductor Wafer Processing System," Ser. No. 09/098,969,
filed Jun. 16, 1998; and is herein incorporated by reference. This
showerhead 120 is connected to a gas panel 130 which controls and
supplies, through mass flow controllers (not shown), various gases
used in different steps of the process sequence. During wafer
processing, a purge gas supply 104 also provides a purge gas, for
example, an inert gas, around the bottom of the pedestal 150 to
minimize undesirable deposits from forming on the pedestal 150.
TiN Film Deposition
An ideal TiN film should have low stress and good step coverage,
especially for plug filling applications involving small geometries
at or below 0.18 .mu.m. Proper adjustment of deposition process
conditions are required to provide a film with optimal, desirable
characteristics. In the deposition of TiN using a reaction between
NH.sub.3 and TiCl.sub.4, for example, the NH.sub.3 :TiCl.sub.4
ratio can be adjusted to provide TiN films with varying step
coverage and stress characteristics.
In a typical TiN deposition process, a pedestal temperature of over
650.degree. C. is often used at a typical NH.sub.3 :TiCl.sub.4
ratio of about 5. This results in a TiN film having a tensile
stress on the order of 2.times.10.sup.10 dyne/cm.sup.2 for a 200
.ANG. thick film. Cracks begin to develop in these films that are
about 400 .ANG. thick. In general, TiN film stress can be reduced
by lowering the deposition temperature and/or increasing the
NH.sub.3 :TiCl.sub.4 ratio. However, an increased NH.sub.3
:TiCl.sub.4 ratio also leads to a decreased step coverage.
A commonly-assigned application, Ser. No. 09/330,696, entitled
"Method of Depositing a Thick Titanium Nitride Film", filed on Jun.
11, 1999, discloses a method of forming a thick crack-free TiN
layer using a reaction between NH.sub.3 and TiCl.sub.4, and is
herein incorporated by reference.
The present invention provides another embodiment of forming a
thick, low stress TiN layer with good step coverage and low
resistivity. In particular, the method includes the following
features: 1) a relatively low deposition temperature of less than
about 600.degree. C.; 2) an NH.sub.3 :TiCl.sub.4 ratio of at least
about 5, preferably about 8.5; and 3) H.sub.2 plasma treatment of
the deposited film.
Two alternative TiN film deposition recipes are illustrated in
Table 1.
TABLE 1 Process Parameters for TiN Deposition Process (a) Pre-
Process (b) ferred (range) Preferred (range) NH.sub.3 (sccm) 100
(30-200) 150 (100-500) N.sub.2 (sccm) 2000 (1000-5000) 2000
(1000-5000) TiCl.sub.4 (sccm) 12 (3-25) 1.8 (1-6) N.sub.2 (sccm)
1000 (500-2500) 1000 (500-2500) He (sccm) 1000 (500-2500) 1000
(500-2500) NH.sub.3 :TiCl.sub.4 8.5 (2.5-17) 85 (20-250) Pedestal
Temp. (.degree. C.) 580 (400-600) 580 (400-600) Pressure (torr) 20
(5-50) 20 (5-50) Ar Purge (sccm) 2000 (1000-5000) 2000
(1000-5000)
FIGS. 2a-c illustrate schematically cross-sectional views of a
substrate 200 at different stages of an integrated circuit
fabrication sequence. In general, the substrate 200 refers to any
workpiece upon which film processing is performed, and a substrate
structure 250 is used to generally denote the substrate 200
together with other material layers formed upon the substrate 200.
Depending on the specific stage of processing, the substrate 200
may correspond to a silicon semiconductor wafer, or other material
layer which has been formed upon the wafer. FIG. 2a, for example,
illustrates a cross-sectional view of a substrate structure 250,
having a material layer 202 that has been conventionally formed and
patterned (e.g., by lithography and etch) upon the substrate 200.
The material layer 202 may be an oxide (e.g., SiO.sub.2), that has
been patterned to form a contact hole 202H extending to the top
surface 200T of the substrate 200. In general, the substrate 200
may be a layer of silicon, silicides, or other materials. FIG. 2a
illustrates one embodiment in which the substrate 200 is silicon,
and a silicide layer 201, e.g., titanium silicide (TiSi.sub.x),
among others, has been formed at the bottom 202B of the contact
hole 202H. The TiSi.sub.x layer 201 may be formed, for example, by
depositing Ti (e.g., by physical vapor deposition or CVD) over the
silicon substrate 200 and the patterned oxide 202, followed by a
high temperature anneal, which results in the formation of the
TiSi.sub.x, layer 201. The unreacted Ti layer 203 remains over the
top 202T of the oxide layer 202 (no Ti is formed at the side 202S
of the contact hole 202H because of non-conformal Ti deposition.)
FIG. 2b depicts a TiN layer 204 deposited upon the substrate
structure 250 of FIG. 2a.
In one embodiment of the present invention, the TiN film 204 is
formed in a CVD chamber similar to chamber 100 of FIG. 1, using a
reaction between NH.sub.3 and TiCl.sub.4 according to the recipe of
process (a) in Table 1. After a wafer 190 having the substrate
structure 250 is loaded onto the wafer support pedestal 150,
NH.sub.3 and TiCl.sub.4, along with other gases, are introduced
into the chamber 100 for TiN film deposition. TiCl.sub.4 is
introduced, along with helium (He) and nitrogen (N.sub.2), via one
gas line (not shown) of the dual-gas showerhead 120. TiCl.sub.4,
being a liquid at room temperature, is delivered to the gas line
using, for example, a liquid injection system (not shown). In
general, the following gas flow ranges can be used--TiCl.sub.4 :
about 3 to about 25 sccm (calibrated from liquid flow rate), He:
about 500 to about 2500 sccm, and N.sub.2 : about 500 to about 2500
sccm. He and N.sub.2 are generally referred to as "dilutant" gases.
The use of He and N.sub.2 is for illustrative purpose only, and
other gases such as argon (Ar) and hydrogen (H.sub.2) can also be
used as dilutant gases. NH.sub.3, in a flow range of about 30 to
about 200 sccm, is introduced into the chamber 100, along with a
dilutant gas such as N.sub.2 in a range of about 1000 to about 5000
sccm, via the second gas line of the dual-gas showerhead 120. The
dilutant gases in either gas line can comprise either a single gas,
or more than one gas in different combinations or ratios, i.e., as
a gas mixture. While the exact ratio or combination of dilutant
gases is not critical to the practice of the invention, it is
preferable that the some "balance" be maintained between the
respective gas flows in the first and second gas lines. By
maintaining approximately equal gas flows in the two gas lines,
potential "back flow" problems can be avoided.
More preferably, the TiN deposition is performed at an NH.sub.3
flow of about 100 sccm and N.sub.2 flow of about 2000 sccm in the
first gas line, and a TiCl.sub.4 flow of about 12 sccm, N.sub.2
flow of about 1000 sccm and He flow of about 1000 sccm in the
second gas line. In general, an NH.sub.3 :TiCl.sub.4 flow ratio of
greater than about 5 is used, and preferably, about 8.5. A total
pressure greater than about 5 torr, e.g., in a range of about 10 to
about 50 torr, and preferably about 20 torr can be used; and a
pedestal temperature is maintained at about 400-600.degree. C.,
e.g., between 500-600.degree. C., and more preferably about
550-600.degree. C. Depending on the specific process conditions,
the substrate temperature may be about 30-40.degree. C. lower than
the pedestal temperature. Furthermore, a bottom inert gas purge
flow (e.g., Ar or other inert gases) of about 2000 sccm, or more
generally, between about 1000 to about 5000 sccm, is also
established via a separate gas line and a purge gas supply 104
provided at the bottom of the chamber 100. Aside from minimizing
the accumulation of undesirable deposits at the back of the wafer
support pedestal 150, the purge gas flow may also affect deposition
uniformity.
Under these process conditions, a crack-free TiN layer 204, having
a film stress of less than about 1.times.10.sup.10 dynes/cm.sup.2
can be formed with a step coverage of over 95% over a contact hole
with a near-vertical sidewall and an aspect ratio of about 7.
(Aspect ratio is defined in this illustration by the ratio of the
depth d to the width w of the contact hole 202H.) Using this
deposition process alone, the TiN layer 204 can be formed into a
TiN plug (not shown) inside the contact hole 202H by an appropriate
planarization technique, e.g., blanket etchback or chemical
mechanical polishing. With a depositing temperature below about
600.degree. C., step coverage can be improved for contact with high
aspect ratios, e.g., over 7:1. For features with even higher aspect
ratios, it may also be necessary to further improve the step
coverage by decreasing the NH.sub.3 :TiCl.sub.4 flow ratio.
It should be noted that the formation of a crack-free TiN film is
not solely a function of film stress. Instead, the NH.sub.3
:TiCl.sub.4 ratio at which deposition takes place also plays an
important role. For example, films having the same film stress may
exhibit different "cracking" behaviors if they are deposited using
different NH.sub.3 :TiCl.sub.4 ratios. This may be attributed to
the different surface reactions during deposition and orientation
of the deposited films.
Depending on the deposition temperature and the NH.sub.3
:TiCl.sub.4 ratio, the as-deposited TiN film may have a chlorine
content as high as about 5%. In accordance with the present
invention, the TiN layer 204 is subjected to a plasma treatment
step, as illustrated in FIG. 2c. In particular, the TiN layer 204,
e.g., having a thickness up to about 300 .ANG., is exposed to a
hydrogen-containing plasma 210 by applying a RF power to the
showerhead 120 of chamber 100. The hydrogen-containing plasma 210
is preferably generated from molecular H.sub.2 gas, but may
optionally contain nitrogen (N.sub.2). Other hydrogen-containing,
organic or inorganic precursors, e.g., ammonia gas (NH.sub.3),
methane (CH.sub.4), among others, may also be used in generating
the hydrogen-containing plasma 210. It is believed that the
exposure of the TiN layer 204 to the plasma results in an
interaction between atomic hydrogen (e.g., may include both atomic
neutrals and ions) and the chlorine species in the TiN layer 204.
It is further believed that the film treatment relies more on
chemical interactions rather than ion bombardment. Thus, according
to the present invention, the film treatment can also be performed
under a remote plasma environment, in addition to a local plasma
generated in the vicinity of the substrate.
FIG. 5 illustrates schematically a remote plasma source 501
connected to the chamber 100 for treating a wafer 190 containing
the TiN layer 204 of FIG. 2c. For example, a remote plasma may be
generated by microwave or RF excitation of a plasma source gas
(e.g., a hydrogen-containing gas, along with an inert gas such as
argon). A gas flow controller 505 controls the supply of the plasma
source gas from a gas supply 503 to the remote plasma source 501.
The radical species generated in the remote plasma source 501,
e.g., atomic hydrogen, are introduced into the chamber 100 at an
inlet 507. Chemical interactions occur between radicals from the
plasma and chlorine species in the TiN layer 204, resulting in the
treatment of the TiN layer 204.
Table 2 illustrates the typical process conditions for the H.sub.2
plasma treatment--H.sub.2 flow rate in the range of about 500-5000
sccm, or preferably about 2000 sccm; a pressure range of about
0.5-10 torr, or preferably about 5 torr, with an RF power in the
range of about 600-900 W, or preferably about 600 W. Alternatively,
a H.sub.2 /N.sub.2 plasma may also be used, for example, with a
N.sub.2 flow rate in the range of about 500-5000 sccm. The N.sub.2
/H.sub.2 flow ratio is typically maintained in a range of about
0-2, and preferably, about 1; and a 40 seconds treatment time is
typically used for a 300 .ANG. thick TiN film. A shorter treatment
time may suffice for a thinner TiN film. Optionally, other inert
gases, such as Ar or helium (He) may also be added to the treatment
plasma. For treatment using a remote plasma, the process conditions
(e.g., plasma power, gas flow rate, pressure, and so on) may be
adjusted to provide a sufficient amount of atomic hydrogen to reach
the TiN layer 204 for effective treatment. The amount of radical
species needed for such treatment may be found by experimentation
by one skilled in the art.
TABLE 2 Plasma Treatment Process Parameters Plasma Treatment
Preferred (range) H.sub.2 (sccm) 2000 (500-5000) N.sub.2 (sccm)
2000 (500-5000) (optional) Pedestal Temp. (.degree. C.) 580
(400-600) Pressure (torr) 5 (0.5-10) RF power (W) 600 (600-900) Ar
Purge (sccm) 500 (200-1000)
The plasma treatment using a hydrogen-containing plasma, such as
that generated from H.sub.2, is more effective in reducing the Cl
content in TiN films compared to thermal annealing in NH.sub.3. For
example, at a temperature of about 580.degree. C., a TiN film has a
Cl concentration of about 3% after NH.sub.3 thermal anneal,
compared to about 1.5% after a H.sub.2 /N.sub.2 plasma treatment.
Typically, the resistivity of a TiN film treated in a H.sub.2
/N.sub.2 plasma, or more generally, a plasma comprising hydrogen
and nitrogen, at about 580.degree. C. is less than about 200-230
.mu.ohm-cm. In one embodiment, for example, a TiN film treated with
a plasma comprising hydrogen has a resistivity of about 180
.mu.ohm-cm, compared to about 320 .mu.ohm-cm after NH.sub.3 thermal
anneal.
A more favorable aging effect is also observed for TiN films
treated with a hydrogen-containing plasma compared to thermal
anneal with NH.sub.3. For example, TiN films treated with a H.sub.2
plasma exhibit less than 4% increase in sheet resistance after 24
hours, while other TiN films of the same thickness treated by
thermal annealing in NH.sub.3 show an increase of about 40%.
In certain embodiments, it is observed that after the plasma
treatments, the stoichiometry or Ti:N ratio of the TiN film has not
been modified, and there is no significant film densification.
However, since the TiN film deposited at a relatively low
temperature tends to be amorphous or micro-crystalline, the plasma
treatment may have the effect of enhancing the TiN grain size, or
causing minor changes in the crystal orientation.
In another aspect of the invention, the film deposition and plasma
treatment steps are performed in different sequence combinations in
order to achieve various desirable film properties. One specific
fabrication sequence, for example, involves the formation of a
composite TiN layer using a two-step procedure that uses different
deposition conditions in the two process steps. This process
sequence is illustrated in FIGS. 3a-d. FIG. 3a shows the deposition
of a first TiN layer 304 upon a substrate structure 350 similar to
that shown in FIG. 2c. The TiN layer 304 is preferably a relatively
low stress film that is also relatively thin, e.g., less than about
20-25 .ANG.. For example, the recipe of process (b), shown in Table
1, may be used to deposit this layer 304 at a temperature of less
than about 600.degree. C. An NH.sub.3 :TiCl.sub.4 flow ratio of
greater than about 20, preferably 40, or more preferably 85, is
used in this step to provide a first layer with relatively low
stress. In the second step of the process sequence, a second TiN
layer 306 is deposited upon the first layer 304, as shown in FIG.
3b. The second TiN layer 306 is preferably deposited under process
conditions that favor a good step coverage, for example, at an
NH.sub.3 :TiCl.sub.4 flow ratio greater than about 5, or more
preferably about 8.5, as shown in the process recipe (a) of Table
1. This second TiN layer 306 may be deposited to a thickness up to
about 300 .ANG., and may have a film stress that is higher than
that of layer 304. FIG. 3c shows the as-deposited TiN layer 306
being exposed to a hydrogen-containing plasma 310, such as that
generated from H.sub.2. This plasma treatment results in a
composite TiN layer 314 shown in FIG. 3d, comprising the plasma
treated or modified layer 306m, which has a reduced Cl content
compared to the as-deposited layer 306 of FIG. 3c, and the
underlying TiN layer 304. Depending on the specific plasma
condition and the thickness of the second TiN layer 306, the
underlying layer 304 may or may not be treated by the plasma. For
example, if the layer 306 has a thickness less than about 250
.ANG., the layer 304 will be partially treated by the plasma 310.
For a layer 306 thicker than about 250 .ANG., the layer 304 will
probably not be treated. However, since the first TiN layer 304 has
a lower chlorine content than the second TiN layer 306 (layer 304
is deposited under a higher NH.sub.3 :TiCl.sub.4 ratio condition),
whether the layer 304 is plasma treated or not will not
significantly affect the resistivity of the composite layer 314.
After plasma treatment according to the embodiments of the present
invention, there is no noticeable film densification, and the
composite layer thickness t.sub.c is approximately equal to the sum
of the thickness of the as-deposited TiN layers 304 and 306.
Additional cycles of film deposition and plasma treatment can be
performed as needed to form a composite TiN layer of desired
thickness. In accordance with the present invention, for example, a
crack-free, TiN layer 314 having a thickness of over 1000 .ANG. can
be fabricated for use in plug fill applications.
In general, a composite TiN layer of desired thickness may be
formed from an aggregate of TiN component layers by repeating
several cycles of film deposition and plasma treatment.
Optimization of the deposition and plasma treatment conditions for
individual TiN components layers will result in a composite TiN
layer having the combined advantages of improved step coverage and
reduced film stress.
Aside from plug fill applications, the TiN layer formed by the
present process may also be used as a barrier layer for an upper
electrode in a capacitor structure having tantalum pentoxide
(Ta.sub.2 O.sub.5) as the dielectric. FIG. 4 illustrates a
cross-sectional view of such a capacitor structure.
The bottom electrode 400 may comprise of silicon, e.g.,
polysilicon. A barrier layer 402 such as silicon nitride may also
be used prior to the formation of the dielectric layer 404
comprising Ta.sub.2 O.sub.5. Typically, Ta.sub.2 O.sub.5 may be
formed by a CVD process using a liquid source, e.g.,
tantalum-pentaethoxy (TAETO) or tantalum-tetraethoxydimethylamine
(TATDMAE), at a temperature of less than about 450.degree. C. A TiN
barrier layer 406 is then formed upon the Ta.sub.2 O.sub.5
dielectric layer 404, preferably at a low processing temperature so
as to avoid undesirable inter-diffusion across the various material
layers. This can be achieved, for example, by the process of the
present invention. The TiN barrier layer 406 can be deposited using
the recipe shown in Table 1, followed by treating in a plasma
generated from H.sub.2. An upper electrode layer 408, which may
comprise polysilicon or other suitable conducting materials, is
then formed upon the plasma treated TiN barrier layer 406, thus
resulting in the capacitor structure of FIG. 4.
While the present invention is particularly well-suited for
applications requiring thick film formation (e.g., plug fill), it
is generally applicable to many other substrate structures
encountered in various stages of integrated circuit fabrication,
including liner/barrier, capacitor, and so on.
Although several preferred embodiments which incorporate the
teachings of the present invention have been shown and described in
detail, those skilled in the art can readily devise many other
varied embodiments that still incorporate these teachings.
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